CN100553385C

CN100553385C - Thermatron

Info

Publication number: CN100553385C
Application number: CNB2005800176737A
Authority: CN
Inventors: 末永治雄; 守屋英明; 酒井伸一; 森川久; 松仓丰继; 城川信夫
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 2004-04-07
Filing date: 2005-04-04
Publication date: 2009-10-21
Anticipated expiration: 2025-04-04
Also published as: US20070195561A1; EP1734791A1; EP1734791A4; WO2005099309A1; CN1961612A; JP4142609B2; EP1734791B1; US8217323B2; JP2005302375A

Abstract

Might provide can be by adding a kind of inverter circuit that ball bearing made using is carried out smooth starting.A kind of magnetron-driving high-frequency heating is provided, and wherein DC power supply is blocked by two thyristors and is exchanged output via resonant circuit.This thermatron comprises generative circuit idle time that is used for disconnecting simultaneously semiconductor element.The driver part that is used to drive this thyristor has the function that restriction is used to drive the low-limit frequency of this thyristor.When the operation of this thermatron began, this low-limit frequency was set to height, reduced the setting of this low-limit frequency then gradually.

Description

Thermatron

Technical field

The present invention relates in microwave oven etc., use the high-frequency heating of magnetron, relate in particular to the inverter circuit that is used for this.

Background technology

The conventional power source that is installed on the high-frequency heating apparatus is heavy and big.Therefore had and made the lighter requirement of the littler weight of power supply size.For this reason, in various types of current fields, will switch (switching) energetically and be applied to power supply the power supply size is littler, weight is lighter and price is lower to make thus.Coming in the thermatron of cooking food by the microwave that generates by magnetron, existing to make the littler and lighter requirement of weight of size of the power supply that is used to drive magnetron.This requirement realizes by the switching in the inverter circuit.

In the inverter circuit, the present invention at high frequency inverter circuit based on the resonant circuit system that uses switching device, wherein the arm of electric bridge forms (for example, referring to patent documentation 1) by two transistors.

Patent documentation 1:

The open 2000-58252 of Japan Patent

For a transistorized inverter (the control on/off at interval), must use withstand voltage about 1, the 000 volt transistor of collector electrode-emitter.Yet in two transistorized bridge arrangement, it is withstand voltage that each transistor needn't have high collector electrode-emitter.Therefore, the withstand voltage about 600V of each transistorized collector electrode-emitter is just enough.Therefore, advantageously can in this bridge arrangement, use transistor at a low price.In such inverter, resonant circuit is formed by inductance L and capacitor C, and this resonant circuit has as shown in Figure 1, peak value is in the resonance characteristic at resonance frequency f0 place.

Fig. 1 be illustrate when constant voltage being applied to according to inverter resonant circuit of the present invention, electric current is to the diagram of operating frequency characteristic.

Frequency f 0 is the resonance frequency of the LC resonant circuit in the inverter circuit.The electric current of use in the frequency range f1-f3 that is higher than this frequency f 0 is to frequency characteristics 11.

Electric current I 1 is the highest at resonance frequency f0 place.Electric current I 1 is increased to f3 along with the f1 of frequency from frequency range and reduces.In frequency range f1-f3, low more frequency approaches resonance frequency more.Therefore, electric current I 1 increases so that increase the electric current that flows into the leakage transformer primary side.On the contrary, high more frequency is more away from resonance frequency.Therefore, the electric current that flows into the leakage transformer primary side reduces.Inverter circuit at the microwave oven that is used for having operated the nonlinear load effect changes output by changing this frequency.

In the microwave oven of the nonlinear load that uses magnetron, as described later, when the power supply that will import was AC power such as industrial power, switching frequency changed.

In any high frequency output, be the highest near 90 degree and 270 frequencies of spending phase places.For example, when the power with 200W used microwave oven, highest frequency was near f3.When power was 500W, highest frequency was lower than f3, and when power be 1, during 000W, highest frequency further reduces.Though cannot say for sure, because input power or input current control, this frequency changes according to the change of industrial power voltage, magnetron temperature etc.

In addition, in above-mentioned power phase near 0 degree and 180 degree places, unless applied high pressure, otherwise the higher-order of oscillation can not appear.According to this specific character of magnetron, be near the f1 place with frequency configuration, the resonance frequency f0 that the close wherein resonance current of this f1 increases.Therefore, increased, can utilize it from magnetron, to generate the phase width of the industrial power of radio wave so that be provided with widely with respect to industrial power, the step-up ratio that is applied to the voltage of magnetron.

Fig. 2 shows the example of the resonant mode high-frequency heating apparatus that is driven by patent documentation 1 disclosed two transistored bridge switching devices.In Fig. 2, high-frequency heating apparatus is made of DC power supply 1, leakage transformer 2, first semiconductor switching device 6, first capacitor 4, second capacitor 5, the 3rd capacitor (smmothing capacitor) 13, second semiconductor switching device 7, drive part 8, full-wave voltage doubler circuit 10 and magnetron 11.

1 pair of industrial power of DC power supply carries out full-wave rectification, and the direct voltage VDC that is obtained is applied to the series circuit that is made of the elementary winding 3 in second capacitor 5 and the leakage transformer 2.First semiconductor switching device 6 and second semiconductor switch 7 are connected in series.The series circuit and second semiconductor switching device 7 that are made of the elementary winding 3 in the leakage transformer 2 and second capacitor 5 are connected in parallel.

First capacitor 4 and second semiconductor switch 7 are connected in parallel.The high pressure output that generates in the secondary winding 9 in leakage transformer 2 is converted to High Level DC Voltage by full-wave voltage doubler circuit 10, and is applied between the anode and negative electrode of magnetron 11.The tertiary winding 12 of leakage transformer 2 offers electric current on the negative electrode of magnetron 11.

First semiconductor switching device 6 is made of IGBT and the fly-wheel diode that is connected in parallel with it.Second semiconductor switching device 7 is made of in an identical manner IGBT and diode.

Though cannot say for sure, first and second

semiconductor switching devices

6 and 7 are not limited to this type.Also can use thyristor, GTO switching device etc.

Drive part 8 has oscillating part in inside, and this oscillating part is used to generate the drive signal that is used for first semiconductor switching device 6 and second semiconductor switching device 7.Generate signal by this oscillating part, and give first semiconductor switching device 6 as drive signal this signal with preset frequency and predetermined load.

First and second

semiconductor switching devices

6 and 7 are perhaps driven first and second

semiconductor switching devices

6 and 7 the two idle time that all disconnect (dead time) with wherein at interval by driven.Idle time is by after a while the generation unit of describing idle time being provided.After the disconnection of one of first and second

semiconductor switching devices

6 and 7, the end-to-end voltage of another semiconductor switching device is high.When connecting described another semiconductor switching device in this case, can flow through the overcurrent of similar spike so that unnecessary loss and noise occur.When be provided idle time, postpone and connecting, till this end-to-end voltage is reduced to about 0V.Thus, above-mentioned loss and noise have been prevented.Though do not say, when oppositely switching, carry out similar operation yet.

Fig. 3 shows the pattern that the circuit among Fig. 2 is operated respectively.

In addition, Fig. 4 shows the voltage-to-current oscillogram of the various piece such as semiconductor switching device etc. in the circuit.

In the figure, (a) in pattern 1, give drive signal to first semiconductor switching device 6.In this case, flow through the elementary winding 3 and second capacitor 5 of leakage transformer 2 from the electric current of DC power supply 1.

(b) in pattern 2, first semiconductor switching device 6 disconnects, and the electric current that has flow through the elementary winding 3 and second capacitor 5 begins to flow to first capacitor 4, and the voltage of first semiconductor switching device 6 increases simultaneously.

(c) in mode 3, the voltage of first capacitor 4 moves to 0V from VDC.In mode 3, the end-to-end voltage of first capacitor 4 reaches 0V, and constitutes the diode connection of second switch device 7.

(d) in pattern 4, the sense of current that has flow through the elementary winding 3 and second capacitor 5 is reversed by resonance.Therefore, before this incident, second semiconductor switching device 7 must be connected always.In the period of

pattern

2,3 and 4, the voltage of first semiconductor switching device 6 becomes and equals DC power supply voltage VDC.In the zone such as Europe, the effective value of industrial power voltage is 230V, and voltage peak reaches

Doubly.Therefore, DC power supply voltage VDC is approximately 325V.

(e) in pattern 5, second semiconductor switching device 7 disconnects, and the electric current that has flow through second capacitor 5 and elementary winding 3 begins to flow to first capacitor 4, so that the voltage of first capacitor 4 is increased to VDC.

(f) in pattern 6, the voltage of first capacitor 4 reaches VDC, so that constitutes the diode connection of first semiconductor switching device 6.The sense of current that has flow through the elementary winding 3 and second capacitor 5 is reversed by resonance.Before this incident, first semiconductor switching device 5 must be connected always.This causes pattern 1.In the period of

pattern

6 and 1, the voltage of second semiconductor switching device 7 becomes and equals DC power supply voltage VDC.

According to this circuit arrangement, the voltage peak that be applied to first semiconductor switching device 6 and second semiconductor switching device 7 can become and equate with DC power supply voltage VDC.

Pattern 2 and pattern 5 are the resonance periods that wherein flow into first capacitor 4 and second capacitor 5 from the electric current of elementary winding 3.Because the capacitance of first capacitor 4 be set to not to be higher than second capacitor 5 capacitance 1/10, so the electric capacity of combination is basically near the capacitance of first electric capacity 4.The voltage that will be applied to first semiconductor switching device 6 and second semiconductor switching device 7 in

mode

3 and 5 is changed by the time constant of the impedance of depending on this combination capacitor and leakage transformer 3.Because changing, this voltage has the tendency that depends on above-mentioned time constant, so the switching loss when first semiconductor switching device in mode 3 disconnects has alleviated.

In addition, this voltage reaches zero in pattern 5.Therefore, be zero because in pattern 1, when first semiconductor switching device is connected, be applied to the voltage of first semiconductor switching device, so the switching loss when first semiconductor switching device is connected has alleviated.This is called zero voltage switch.The characteristics of this resonant circuit system comprise these.This system has carried out maximum use to this characteristic, and has the advantage that the voltage that prevents each semiconductor switching device is higher than DC power supply voltage VDC.As shown in Figure 4, second capacitor 5 is set to have enough big so that suppress the capacitance of the fluctuation (ripple) of its voltage.

As shown in Figure 2,

semiconductor switching device

6 and 7 be connected in series circuit and DC power supply 1 are connected in parallel so that form in the inverter circuit of the arm that is made of two transistors therein,

semiconductor switching device

6 and 7 replaces and repeatedly switches on and off, so that in the elementary winding 3 of leakage transformer 2, generate high-frequency alternating current, and in the secondary winding 9 of leakage transformer 2, respond to high pressure and high frequency.Any period that is in simultaneously when connecting when

semiconductor switching device

6 and 7 all is unacceptable, though this period be one second also be like this.This is because the short circuit of DC power supply 1 occurs in such period.

Therefore, in background technology, always after one of

semiconductor switching device

6 and 7 disconnect and before another semiconductor switching device connection, the period (be abbreviated as DT idle time) that provides wherein semiconductor switching device 6 and semiconductor switching device 7 all to disconnect.

Therefore, will DT idle time be described with reference to figure 4.

Fig. 4 shows first and second semiconductor switching devices 6 in above-mentioned pattern 1 to 6 and the voltage and current waveform in 7 (Fig. 2) and first and

second capacitors

4 and 5.

(a) among Fig. 4 shows the current waveform of first semiconductor switching device 6 in above-mentioned pattern 1 to 6, wherein begin the semiconductor switching device 6 just connected (therefore from time t0, in (b) of Fig. 4, the emitter-collector voltage of semiconductor switching device 6 is zero) time 1 place when pattern 1 finishes disconnects (electric current vanishing thereunto).

On the other hand, (d) among Fig. 4 shows the current waveform of second semiconductor switching device 7, wherein second semiconductor switching device 7 that begins to have disconnected from time t0 keeps disconnecting, till the time t2 when having applied connection signal and mode 3 to it and begin.

Therefore, among the period DT1 between time t1 and time t2, the two has all disconnected first semiconductor switching device 6 and second semiconductor switching device 7.

This period DT1 is corresponding to desired minimum value idle time.Maximum is the period between time t1 and time t3.Be allowed to idle time in this scope.

With the same manner, at the period DT2 between time t4 shown in Fig. 4 (c), when second semiconductor switching device 7 disconnects (electric current vanishing thereunto) and the time t5 when shown in (a) among Fig. 4, with connection signal, being applied to first semiconductor switching device 6 and pattern 6 and beginning corresponding to this minimum value.Maximum is the period between time t4 and time t6.Be allowed to idle time in this scope.

In two transistorized inverter circuits in background technology, based on period DT1 and DT2, this idle time, the value of DT was fixed, and these two period DT1 and DT2 obtain from the scope that switches on and off mutual superposition not that makes

semiconductor switching device

6 and 7 respectively.

Yet, in the inverter circuit of microwave oven, when driving this inverter circuit with high frequency region, the period between time when one of semiconductor switching device is disconnected and the time when the emitter-collector voltage Vce of another semiconductor switching device drops to zero has increased.Therefore, when disconnect from above-mentioned semiconductor switching device beginning over and done with fixedly after idle time, when connection signal is applied to above-mentioned another semiconductor switching device, above-mentioned another semiconductor switching device drops at emitter-collector voltage Vce and is switched on before zero.When switching frequency is high, thermal losses may appear in semiconductor switching device, and this causes the fault of semiconductor switching device or the appearance of the noise that produced by the spike electric current.

Also will the reason that thermal losses occur and noise occurs be described with reference to figure 4.

Though the time t1 place of semiconductor switching device 6 in Fig. 4 (a) disconnected (electric current vanishing thereunto), in (d) of Fig. 4, need time t1-t2 to allow the end-to-end voltage (solid line) of another semiconductor switching device 7 drop to zero.Therefore, when when time t2 is applied to another semiconductor switching device 7 with connection signal, semiconductor switching device 7 begins to connect (setting up conductivity) (this is called " zero volt switch ") from no-voltage, and this is because the emitter-collector voltage of semiconductor switching device 7 had dropped to zero before that time.Therefore, the problem of thermal losses and noise can not occur.

Yet the trapezoidal gradient of VDC changes according to the intensity of resonance.When resonance strong (frequency is low), this gradient is very steep, so that the end-to-end voltage of semiconductor switching device 7 reaches zero fast.When a little less than the resonance when (frequency height), this gradient is very mild, so that needs more time to allow end-to-end voltage drop to zero volt.When such high frequency region drives this inverter circuit, this frequency is elongated away from resonance frequency so that time constant.Therefore, in (d) of Fig. 4, the end-to-end voltage (shown in dotted line) of another semiconductor switching device 7 drops to time of zero and has been elongated, so that this voltage can not descend in time t1-t2 fully.Therefore, even after time t2, also applied predetermined voltage (referring to by the Vt2 shown in the dotted line F).

Therefore, when as usual when time t2 is applied to semiconductor switching device 7 with connection signal, this semiconductor switching device 7 is switched on, and predetermined voltage Vt2 is applied between the emitter and collector of semiconductor switching device 7.Therefore, thermal losses has appearred.In addition, owing to the appearance of big dv/dt value causes flowing through steep spike electric current, consequently produce noise.

Even when carrying out such direct-cut operation (executing switching though voltage or electric current are non-vanishing), also guarantee this idle time.Therefore, direct-cut operation does not cause any fault such as power supply short circuit, but only occurs the waste heat loss in IGBT.Such thermal losses is cooled off by heat dump.Even when thermal losses occurring, also can normally keep the operation of inverter.The noise that causes owing to the spike electric current is not the value that be taken as serious problems.Therefore, in the background technology inverter circuit, the side effect of hard switching is out of question at all.Therefore, considered such inverter circuit, wherein change in background technology be fix idle time DT to save useless energy consumption, the useful life of semiconductor switching device is free from side effects, and noise occurs hardly.

Summary of the invention

The problem to be solved in the present invention

Therefore, the objective of the invention is not only smooth start to be applied to idle time wherein DT and be the high-frequency heating apparatus of fixing type, and apply it to the high-frequency heating apparatus of the type that DT changes according to frequency idle time wherein, and such high-frequency heating apparatus is provided, wherein, very easy circuit just can easily realize smooth start by being increased to wherein.

The means of dealing with problems

In order to address the above problem, according to a first aspect of the invention, a kind of high-frequency heating apparatus that is used to drive magnetron is provided, comprise: DC power supply, it comprises AC power, is used for the voltage of this AC power is carried out the rectification circuit of rectification and is used for the smoothly smmothing capacitor of the output voltage of this rectification circuit; Series circuit comprises two semiconductor switching devices, and described series circuit and described AC power are connected in parallel; Resonant circuit is connected to the elementary winding and the capacitor of leakage transformer, and an end of described resonant circuit is connected to the mid point of the above-mentioned series circuit in the AC equivalent electric circuit, and the other end of described resonant circuit is connected to an end of described AC power; Driver element is used to drive each described semiconductor switching device; Rectification unit is connected to the secondary winding of described leakage transformer; Magnetron is connected to described rectification unit; And idle time generative circuit, be used for disconnecting simultaneously described semiconductor switching device; This high-frequency heating apparatus is characterised in that: described driver element has the function of the low-limit frequency of the frequency that restriction is used for driving described semiconductor switching device, so that described low-limit frequency is set to height when this high-frequency heating apparatus operation beginning, and described low-limit frequency is set to after this progressively reduce.

According to a second aspect of the invention, a kind of high-frequency heating apparatus that is used to drive magnetron is provided, it comprises: DC power supply, and it comprises AC power, is used for the voltage of this AC power is carried out the rectification circuit of rectification and is used for the smoothly smmothing capacitor of the output voltage of this rectification circuit; Two series circuits, each all comprises two semiconductor switching devices, and each in the described series circuit all is connected in parallel with described AC power; Resonant circuit is connected to the elementary winding and the capacitor of leakage transformer, and an end of described resonant circuit is connected to the mid point of one of described series circuit, and the other end of described resonant circuit is connected to the mid point of another series circuit; Driver element is used to drive each above-mentioned semiconductor switching device; Rectification unit is connected to the secondary winding of above-mentioned leakage transformer; Magnetron is connected to above-mentioned rectification unit; And idle time generative circuit, be used for disconnecting simultaneously described semiconductor switching device; This high-frequency heating apparatus is characterised in that: above-mentioned driver element has the function that restriction drives the low-limit frequency in the used frequency of above-mentioned semiconductor switching device, so that above-mentioned low-limit frequency is set to height when this high-frequency heating apparatus operation beginning, and above-mentioned low-limit frequency is set to after this progressively reduce.

According to a third aspect of the invention we, a kind of high-frequency heating apparatus that is used to drive magnetron is provided, it comprises: DC power supply, and it comprises AC power, is used for the voltage of this AC power is carried out the rectification circuit of rectification and is used for the smoothly smmothing capacitor of the output voltage of this rectification circuit; Series circuit comprises two semiconductor switching devices, and above-mentioned series circuit and above-mentioned AC power are connected in parallel; Resonant circuit is connected to the elementary winding and the capacitor of leakage transformer, and one of above-mentioned resonant circuit and above-mentioned semiconductor switching device are connected in parallel; Driver element is used to drive each above-mentioned semiconductor switching device; Rectification unit is connected to the secondary winding of above-mentioned leakage transformer; Magnetron is connected to above-mentioned rectification unit; And idle time generative circuit, be used for disconnecting simultaneously described semiconductor switching device; This high-frequency heating apparatus is characterised in that: above-mentioned driver element has the function that restriction drives the low-limit frequency in the used frequency of above-mentioned semiconductor switching device, so that above-mentioned low-limit frequency is set to height when the operation of this high-frequency heating apparatus begins, and above-mentioned low-limit frequency is set to after this progressively reduce.

According to aforementioned first to the third aspect the high-frequency heating apparatus of either side also comprise: the error signal generative circuit is used for according at the input current of above-mentioned AC power and the difference generated error signal between the reference current; And FM signal generative circuit, be used for output (error signal) based on above-mentioned error signal generative circuit, and proofread and correct the rectified voltage/redressed current that is obtained by the above-mentioned AC power of rectification, wherein the output of above-mentioned FM signal generative circuit is offered above-mentioned idle time of generative circuit; This high-frequency heating apparatus is characterised in that: insert the low-limit frequency restricting circuits at above-mentioned FM signal generative circuit and above-mentioned idle time between the generative circuit, this low-limit frequency restricting circuits is based on the output signal of above-mentioned FM signal generative circuit and limited frequency is offered above-mentioned idle time of generative circuit, so that the operation at above-mentioned high-frequency heating apparatus begins the place, with the frequency configuration that is provided with of low-limit frequency restricting circuits is the output that is higher than above-mentioned FM signal generative circuit, and according to beginning the over and done with time from operation, progressively reduce above-mentioned limited frequency, when reducing above-mentioned limited frequency, according to the over and done with time, higher signal in the output signal of the switching frequency of above-mentioned limited frequency and above-mentioned FM signal generative circuit is chosen as the signal that will offer above-mentioned idle time of generative circuit, so that selected signal is progressively changed into the output signal of above-mentioned FM signal generative circuit.

Preferably, described high-frequency heating apparatus is characterised in that: above-mentioned low-limit frequency restricting circuits has capacitor, above-mentioned capacitor charges during the pausing operation of above-mentioned high-frequency heating apparatus, and in case above-mentioned high-frequency heating apparatus begins operation, just the voltage of this capacitor is offered above-mentioned idle time of generative circuit, and the electric charge that in this capacitor, accumulates of discharge.

According to aforementioned first to the third aspect the high-frequency heating apparatus of either side be characterised in that: above-mentioned idle time, generative circuit generated idle time fixing or that more or less increase, and did not consider switching frequency.

According to aforementioned first to the third aspect the high-frequency heating apparatus of either side be characterised in that: above-mentioned idle time, generative circuit generated the idle time that the increase along with switching frequency increases.

According to aforementioned first to the third aspect the high-frequency heating apparatus of either side be characterised in that: generative circuit was fixed at the switching frequency place that is not higher than preset frequency or was more or less increased this idle time above-mentioned idle time.

Preferably, described high-frequency heating apparatus is characterised in that: above-mentioned idle time, generative circuit increased idle time suddenly at the switching frequency place that is not less than preset frequency.

Preferably, described high-frequency heating apparatus is characterised in that: in the value fixing or that more or less increase of above-mentioned idle time at the switching frequency place that is not higher than preset frequency or in the value of the unexpected increase of above-mentioned idle time at the switching frequency place that is not less than preset frequency is variable.

Preferably, described high-frequency heating apparatus is characterised in that: the value of above-mentioned predetermined switching frequency is variable.

According to aforementioned first to the third aspect the high-frequency heating apparatus of either side be characterised in that: above-mentioned idle time, generative circuit progressively increased idle time along with the increase of switching frequency.

According to aforementioned first to the third aspect the high-frequency heating apparatus of either side be characterised in that: above-mentioned idle time, generative circuit generated idle time based on the positive and negative offset voltage, in the described positive and negative offset voltage each is to change with proportional first gradient of the increase of switching frequency, and when switching frequency reaches preset frequency or when higher, changes with second gradient.

According to aforementioned first to the third aspect the high-frequency heating apparatus of either side be characterised in that: above-mentioned idle time, generative circuit comprised: the VCC power supply; Load control power supply; First electric current changes pro rata with switching frequency; Second electric current begins to flow and change pro rata with this switching frequency at the preset frequency place; The 3rd electric current obtains by the combination current of above-mentioned two electric currents and pre-determined factor are multiplied each other; Upper and lower electromotive force generation unit is used for generating by adding two upper and lower electromotive forces that above-mentioned load control power supply obtains respectively to the proportional positive and negative offset voltage of above-mentioned the 3rd electric current; And generate idle time based on above-mentioned two upper and lower electromotive forces.

Preferably, described high-frequency heating apparatus is characterised in that: carry out input power or input current control by at least one that changes in above-mentioned load control power source voltage and the above-mentioned switching frequency.

Utilize such configuration, might obtain such inverter circuit, wherein prevent the short circuit of power supply, occur thermal losses among the IGBT hardly, therefore do not have useless energy dissipation, and occur noise hardly; And wherein can realize smooth start by the ball bearing made using of adding the there to.

Description of drawings

Fig. 1 be illustrate according to of the present invention when constant voltage is applied to inverter resonant circuit, electric current is to the diagram of operating frequency characteristic.

Fig. 2 shows the example of patent documentation resonant mode high-frequency heating apparatus 1 disclosed, that driven by two transistorized bridge switches devices;

Fig. 3 shows the pattern that the circuit among Fig. 2 is operated respectively;

Fig. 4 shows the voltage-to-current oscillogram of the various piece such as semiconductor switching device etc. in this circuit;

The high-frequency heating apparatus that Fig. 5 shows according to the present invention, driven by two transistored bridges;

Fig. 6 shows first embodiment of the low-limit frequency restricting circuits that is used to realize smooth start;

Fig. 7 shows second embodiment of the low-limit frequency restricting circuits that is used to realize smooth start;

Fig. 8 is the diagram that is used to illustrate the principle that generates idle time, (a) among Fig. 8 be used to be illustrated in oscillating circuit and idle time generative circuit each output and the diagram of the relation between the output of squaring circuit, (b) among Fig. 8 is the diagram that is used to illustrate such principle, according to this principle, though when frequency changes in this frequency is low scope, idle time DT also fix;

Fig. 9 shows the specific example of generative circuit idle time;

Figure 10 shows the electric current of this of generative circuit to frequency characteristic idle time;

Figure 11 illustrates the diagram of idle time to frequency characteristics, (a) among Figure 11 show wherein when switching frequency is not higher than frequency f 1 unloaded time D T fix or increase more or less and when this switching frequency is not less than preset frequency f1 the unloaded time D T example of increase suddenly; (b) among Figure 11 shows modified example; (one) among Figure 11 (b) shows fixed value that wherein makes idle time or the vertical variable example of the value that more or less increases, (two) among Figure 11 (b) show the variable example of slope idle time that wherein makes in the frequency f 1, and (three) among Figure 11 (b) show the example of the frequency transverse variable that has wherein made breakover point (point of inflection) effect;

Figure 12 shows and wherein makes the second variable embodiment of idle time;

Figure 13 shows the example of the oscillating circuit among Fig. 5;

Figure 14 shows three examples of the resonant mode high-frequency heating apparatus that is driven by two transistored bridge switching devices;

Figure 15 illustrates according to the frequency of inverter circuit of the present invention diagram to phase characteristic; And

Figure 16 shows the diagram of the output voltage of this inverter circuit to phase characteristic.

1 DC power supply

2 leakage transformers

3 elementary windings

4 first capacitors

5 second capacitors

6 first semiconductor switching devices

7 second semiconductor switching devices

8 drive parts

9 secondary winding

10 full-wave voltage doubler circuit

11 magnetrons

12 3 grades of windings

13 the 3rd capacitors

21 error signal generative circuits

22 FM signal generative circuits

221 low-limit frequency restricting circuits

222 capacitors

The 221a transistor

221b, 221d, 221e resistor

The 221c capacitor

The 221f switch

The 221g amplifier

The 221h constant voltage source

23 oscillating circuits

24 idle time generative circuit

25 squaring circuits

26 drive circuits

Embodiment

The high-frequency heating apparatus that Fig. 5 shows according to the present invention, driven by two transistored bridges.

Among Fig. 5, the main circuit of this high-frequency heating apparatus comprises DC power supply 1, leakage transformer 2, first semiconductor switching device 6, first capacitor 4, second capacitor 5, the 3rd capacitor (smmothing capacitor) 13, second semiconductor switching device 7, drive part 8, full-wave voltage doubler circuit 10 and magnetron 11.The configuration of this main circuit is with shown in Figure 2 identical, and the redundancy that will omit is wherein described.

Then, the control circuit that is used to control

semiconductor switching device

6 and 7 comprises: error signal generative circuit 21 is used to obtain at input current Iin with based on the difference between its reference current Ref; FM signal generative circuit 22 is used for generating FM signal according to this error signal generative circuit 21 and AC all-wave signal; Low-limit frequency restricting circuits 221 is used to carry out the smooth start that obtains the object of the invention; Oscillating circuit 23 is used to generate triangular wave carrier; Idle time, generative circuit 24, were used for changing idle time according to the amplitude of switching frequency; Squaring circuit 25, be used for according to the output of the triangular wave of oscillating circuit 23 and idle time generative circuit 24 output VQ7C and VQ8C formation square wave; And switching device drive circuit 26, be used for generating the pulse that is used for the on/off switch device according to the output of squaring circuit 25.The output of switching device drive circuit 26 is applied to the grid level of switching device (IGBT) 6 and 7 respectively.

Fig. 6 shows first embodiment of the low-limit frequency restricting circuits that is used to carry out smooth start.

Among Fig. 6, Reference numeral 221 expressions are according to the low-limit frequency restricting circuits of first embodiment.This low-limit frequency restricting circuits 221 has transistor 221a,

resistor

221b, 221d and 221e, capacitor 221c, switch 221f and amplifier 221g.The emitter of transistor 221a, collector electrode and base stage are connected respectively to resistance 221b, power Vcc and capacitor 221c.The end of resistor 221b is connected to the output of FM signal generative circuit 22, and its other end is connected to the emitter of transistor 221a as mentioned above.The end of capacitor 221c is connected to the base stage of transistor 221a as mentioned above, its other end ground connection.The end of resistor 221e is connected to power Vcc, and its other end is by switch 221f and resistor 221d ground connection.Switch 221f is a normally-closed contact, and it will be connected when this equipment break-off.The terminal of the resistor 221d side of switch 221f is connected to the positive side of capacitor 221c.

Next, the operation of this low-limit frequency restricting circuits 221 will be described with reference to (b) among the figure 6.

Switch 221f is in connection (ON) state during the operation suspension of high-frequency heating apparatus.Therefore, capacitor 221c is charged to by the defined electromotive force of the division ratio of voltage vcc between

resistor

221e and 221d place.Therefore, transistor 221a has high base potential, so that transistor 221a is in on-state.Therefore, export high pressure V11 (V11 Fig. 6 (b)) from the output of low-limit frequency restricting circuits 221.

When high-frequency heating apparatus began operation (t1 among Fig. 6 (b)), switch 221f disconnected (OFF) so that cut off the charging circuit of capacitor 221.Therefore, capacitor 222 begins to discharge by resistor 221d.Therefore, the base potential of transistor 221a gradually reduces, so that the output potential V12 of transistor 221a (V12 among Fig. 6 (b)) progressively descends and draws out curve.(full-wave rectification) output signal of FM signal generative circuit 22 is put into low-limit frequency restricting circuits 221, and make it pass through line or (wired OR) circuit is connected with the output signal of transistor 221a.Therefore, in the output potential of the output potential of transistor 221a and FM signal generative circuit 22 higher one from 221 outputs of low-limit frequency restricting circuits, so that reach the high frequency voltage (V13 among Fig. 6 (b)) of stable state.

Therefore, Fig. 6 (b) show that the high-frequency heating apparatus that is in operation suspension begins to operate and by transition state reach before the stable state, from the output voltage of low-limit frequency restricting circuits 221.

Fig. 7 shows second embodiment of the low-limit frequency restricting circuits that is used to carry out smooth start.

Among Fig. 7, Reference numeral 222 expressions are according to the low-limit frequency restricting circuits of second embodiment.This low-limit frequency restricting circuits 222 has transistor 222a,

resistor

222b, 222d and 222e, capacitor 222c, switch 222f, amplifier 222g and constant-current source 222h.The emitter of transistor 222a, collector electrode and base stage are connected respectively to resistor 222b, power Vcc and capacitor 222c.The end of resistor 222b is connected to the output of FM signal generative circuit 22, and its other end is connected to the emitter of transistor 222a as mentioned above.The end of capacitor 222c is connected to the base stage of transistor 222a as mentioned above, its other end ground connection.The end of resistance 222e is connected to power Vcc, and its other end is by resistor 222d ground connection.Switch 222f is a normally-closed contact, and it will be connected when this equipment break-off.The end of switch 221f is connected to the anode-side of capacitor 222c, and its other end is connected to the contact between resistor 222e and resistor 222d.Constant-current source 222h is connected to the opposite end of capacitor 222c.

Next, the operation of this low-limit frequency restricting circuits 222 will be described with reference to figure 7 (b).

Switch 222f is in connection (ON) state during the operation suspension of high-frequency heating apparatus.Therefore, capacitor 222c is charged to by the division of voltage vcc between

resistor

222e and 222d than defined electromotive force (be subjected to influencing a little of constant-current source 222h, and influence degree depending on the combined impedance of

resistor

222e and 222d and the value of constant-current source).Therefore, capacitor 222c is charged by voltage vcc.Therefore, transistor 222a has high base potential, so that transistor 222a is in on-state.Therefore, export high pressure V11 (V11 Fig. 7 (b)) from the output of low-limit frequency restricting circuits 222.

When high-frequency heating apparatus began operation (t1 among Fig. 7 (b)), switch 222f disconnected (OFF) so that cut off the charging circuit of capacitor 222.Therefore, capacitor 222 begins to discharge by constant-current source 222h.Therefore, the base potential of transistor 222a descends gradually, so that owing to the function of constant-current source 222h makes the output potential V12 (V12 among Fig. 7 (b)) of transistor 222a progressively descend and draw out straight line.The output signal of (full-wave rectification) of FM signal generative circuit 22 is put in the low-limit frequency restricting circuits 222, and it is connected with the output signal of transistor 222a by line or circuit.Therefore, in the output potential of the output potential of transistor 222a and FM signal generative circuit 22 higher one from 222 outputs of low-limit frequency restricting circuits, so that reach the high frequency voltage (V13 among Fig. 7 (b)) of stable state.

Therefore, Fig. 6 (b) show that the high-frequency heating apparatus that is in the operation suspension state begins to operate and by transition state reach before the stable state, from the output voltage of low-limit frequency restricting circuits 222.

The collector voltage of transistor Q8 and Q7 respectively from idle time generative circuit 24 send to squaring circuit 25 (Fig. 5).In addition, also the output of the triangular wave of oscillating circuit 23 is sent to squaring circuit 25.

Squaring circuit 25 has two comparators 251 and 252.The collector voltage VQ8C of transistor Q8 is applied to the inverting input (-) of comparator 251, and, the triangular wave of oscillating circuit 23 is exported be applied to the normal phase input end (+) of comparator 251 and the inverting input (-) of comparator 252 simultaneously the normal phase input end (+) that the collector voltage VQ7C of transistor Q7 is applied to comparator 252.

Not output (zero potential) when each comparator 251,252 is designed to electromotive force when its normal phase input end (+) and is lower than the electromotive force of its inverting input (-), and have output (high potential) during above the electromotive force of its inverting input (-) when its electromotive force of normal phase input end (+).

Idle time, DT can be divided into following three kinds.

(1): make idle time constant (fixing) and and frequency-independent.

This is the method for having used in background technology.

On the contrary, following two kinds (2) and (3) can be envisioned as changed according to switching frequency idle time.

(2): when switching frequency surpassed preset frequency, idle time, the increase according to switching frequency increased continuously.

(3): when switching frequency surpassed preset frequency, idle time was according to the increase of switching frequency and stepping increases.

Then, the circuit that is used for realizing smooth start according to the present invention can be applicable to above-mentioned classification (1) any to (3).

Fig. 8 is the diagram that is used to illustrate the principle that generates above-mentioned idle time (2), and wherein when switching frequency surpassed preset frequency, this idle time, (2) increased continuously according to the increase of switching frequency.(a) among Fig. 8 is the diagram that is used to be illustrated in the relation between the output of oscillating circuit 23 and generative circuit 24 each output idle time and squaring circuit 25.(b) among Fig. 8 be used to illustrate when switching frequency is not higher than preset frequency should idle time the immobilize principle of institute's foundation of DT.

Among Fig. 8, in comparator 252 (referring to Fig. 5), before time t1, the electromotive force VQ7C of normal phase input end (+) surpasses the electromotive force of the triangular wave of inverting input (-).Therefore, semiconductor switching device is connected (output 1).Simultaneously, in comparator 251, the electromotive force of the triangular wave of normal phase input end (+) is lower than the electromotive force VQ8C of inverting input (-).Therefore, this semiconductor switching device disconnects (output 0).

(1) at time t1 place, because the electromotive force VQ7C of normal phase input end (+) is lower than the electromotive force of the triangular wave of inverting input (-), so comparator 252 outputs 0.

(2) from t1 to t4, comparator 252 keeps output 0.

(3) at time t2 place, because the electromotive force of the triangular wave of normal phase input end (+) is higher than the electromotive force VQ8C of inverting input (-), so comparator 251 outputs 1.

(4) from t2 to t3, comparator 251 keeps output 1.

(5) at time t3 place, because the electromotive force of the triangular wave of normal phase input end (+) is lower than the electromotive force VQ8C of inverting input (-), so comparator 251 outputs 0.

(6) at time t4 place, because the electromotive force VQ7C of normal phase input end (+) is higher than the electromotive force of the triangular wave of inverting input (-), so comparator 252 outputs 1.

(7) from t4 to t5, comparator 252 keeps output 1.

(8) at time t5 place, because the electromotive force VQ7C of normal phase input end (+) is lower than the electromotive force of the triangular wave of inverting input (-), so comparator 252 outputs 0.

(9) from t3 to t6, comparator 251 keeps output 0.

After that, repeat similar operation.

The output of

comparator

251 and 252 is applied to switching device (IGBT) drive circuit 26, so that switching

device

6 and 7 is with same sequential on/off.

In such a way, obtain period t1-t2, t3-t4 when switching

device

6 and 7 disconnects simultaneously and t5-t6 as DT idle time.

In background technology, the duration of DT each is constant (fixing) idle time, and and frequency-independent.In order to improve this, idle time DT is changed according to switching frequency.Here, when switching frequency was lower than preset frequency f1, idle time, DT was set to predetermined fixed value (the perhaps value that increases more or less), and when switching frequency during greater than preset frequency f1, DT increase idle time.

Therefore, will describe with reference to figure 8 (b) and when switching frequency is lower than preset frequency f1, make idle time DT become the principle of being scheduled to fixed value institute foundation.

In Fig. 8 (b), when frequency is high (shown in the solid line), with reference to as described in solid line VQ8C, the VQ7C and triangular wave among the figure 8 (a), between VQ8C, VQ7C and triangular wave, set up following relationship as previous.That is to say that at the time t1 place when electromotive force VQ7C is lower than the electromotive force of triangular wave, output becomes 0.At time t2 place, the electromotive force of triangular wave is higher than electromotive force VQ8C, so that output becomes 1.Therefore, guarantee that the period between time t1 and time t2 is DT idle time.

When frequencies go lower, shown in dotted line, this triangular wave becomes the triangular wave that its gradient becomes mild.Therefore, here, in order to obtain identical DT idle time, defined offset voltage so that electromotive force VQ7C and VQ8C are set to respectively be passed in by the triangular wave shown in the dotted line with from intersection point C1 between the vertical line of time t1 and time t2 drafting and electromotive force VQ7C1 and the VQ8C1 of C2.Because resistor R 8 and R7 fix, so that utilize its electric current I that can obtain such offset voltage 8 and I7 to flow into respectively among resistor R 8 and the R7.

In such a way, though when frequency change so that triangular wave when solid line is changed into dotted line, cut two electromotive force VQ7C1 and VQ8C1 at identical time t1 and t2 respectively by the triangular wave shown in the dotted line.Therefore, idle time, DT was constant.

Fig. 9 shows the specific example of generative circuit idle time.

At Fig. 9, Q01, Q02 and Q1-Q8 represent transistor, and R1-R10 represents resistor.Suppose that I1, I3, I4, I5, I6, I7 and I8 specify the electric current that flows through transistor Q1, Q3, Q4, Q5, Q6, Q7 and Q8 respectively, VQ5E, VQ6E and VQ7E specify the emitter electromotive force of transistor Q5, Q6 and Q7, and the collector electrode electromotive force of VQ7C and VQ8C appointment transistor Q7 and Q8.Current mirror circuit comprises transistor Q1 and Q2.In the same way, current mirror circuit comprises transistor Q1 and Q04, transistor Q3 and Q4 and transistor Q05 and Q8 respectively.The output of transistor Q04 is applied to oscillating circuit 23 (Figure 13).

In addition, the emitter side of transistor Q1 and Q3 is connected to Vcc, and its collector electrode side is connected respectively to the collector electrode side of transistor Q01 and Q03.The emitter side of transistor Q01 and Q03 is connected respectively to terminal MOD and terminal DTADD, and terminal MOD and terminal DTADD are respectively by divider resistance ground connection.The base stage of transistor Q01 and Q03 is connected to the emitter side of transistor Q02, and the collector electrode side joint ground of transistor Q02.To be applied to the base stage of transistor Q02 as the control voltage of the frequency of oscillation of the output of FM signal generative circuit 22 (Fig. 5).

According to being provided between Vcc (being 12V here) and the ground apart from the circuit that is connected in series of resistance R 10, resistance R 8, resistance R 7 and resistance R 9 formation of the order that increases gradually from Vcc.In addition, transistor Q8 provides between resistance R 10 and resistance R 8, so that its emitter side is connected to resistance R 10, and the collector electrode side is connected to resistance R 8.In addition, transistor Q7 provides between resistance R 7 and resistance R 9, so that its emitter side is connected to resistance R 9, and the collector electrode side is connected to resistance R 7.Between resistance R 8 and resistance R 7, apply 1/2Vcc (being 6V here).Near this 6V, the pressure drop in the top resistance R 8 is represented as I8 * R8, and the pressure drop in the following resistance per square is represented as I7 * R7.Electric current I 8 and electric current I 7 change according to frequency.Therefore, the pressure drop among resistance R 7 and the R8 changes according to frequency, so that offset voltage VQ8C and VQ7C change near 6V.

The base voltage that constitutes the transistor Q05 of current mirror circuit is applied to the base stage of transistor Q8.When the characteristic of transistor Q05 and Q8 is equal to each other and its resistance value when being equal to each other, relations I 6=I7=I8 and I3=I4 have been set up.

Yet the present invention is not limited to relations I 1=I2, I3=I4 and I6=(I7=I8).If set up proportionate relationship in the middle of them, the present invention is also applicable.

Incidentally, relations I 7=I8 is essential.

Next, with to relevant idle time generative circuit operation be described and (that is to say, when switching frequency is not higher than preset frequency, keep DT idle time constant (perhaps more or less increasing), and when switching frequency is not less than preset frequency, increase DT idle time).

1) reason that does not flow through (that is to say, in the low scope of frequency of oscillation) in the scope of I3, DT idle time constant (perhaps more or less increasing) therein is:

In the scope that does not flow through I3, set up following relationship.

I1＝I2＝I5，

VQ5E=VQ6E=VQ7E, and

I5×R5＝I6×R6＝I7×R9＝I1×R5

Electric current I 8 and the I7 of inflow transistor Q8 and Q7 are expressed as respectively:

I8＝I6＝I1×(R5/R6)

I7＝I1×(R5/R9)

Offset voltage VR8 and VR7 are expressed as respectively:

VR8＝I8×R8＝{I1×(R5/R6)}×R8

＝I1×R5×(R8/R6)

VR7＝I1×R5×(R7/R9)

Because obtain VQ8C and VQ7C, so VQ8C and VQ7C are expressed as by the above-mentioned offset voltage of plus-minus from 6V:

VQ8C＝6V+VR8＝6V+I1×R5×(R8/R6)

VQ7C＝6V-VR7＝6V-I1×R5×(R7/R9)...(1)

In such a way, frequency is that the electric current I 8 in the scope of low (may fix idle time) and the charge/discharge current I1 of I7 and triangular wave have proportionate relationship therein.Therefore, electric current I 8 and I7 can as sometimes with the same big value of charge/discharge current I1 of triangular wave.This can obtain speculum circuit as shown in Figure 9.Electric current I 6 and I8 are in the fixed relationship with respect to electric current I 5, so that electric current I 6 is consistent each other with I8, and electric current I 7 is in the fixed relationship with electric current I 5, so that electric current I 7 and electric current I 8 are consistent.

Figure 10 shows the electric current of variable idle time of generative circuit to frequency characteristic.

Among Figure 10, I1, I3 and I5 indicate the transistor Q1, the Q3 that flow among Fig. 9 and the electric current of Q5 respectively.Electric current I 5 is expressed as I1+I3.

In the low frequency that is not higher than f1, electric current I 1 (15) is fixed value (I51) or the value (I52) that more or less increases.On the other hand, frequency is not less than in the scope of f1 therein, and electric current I 3 begins sharply to flow through as breakover point with frequency f 1.Therefore, the electric current I 5 as I3 and I1 sum increases suddenly.

Expression formula (1) and Figure 10 according to above-mentioned VQ8C and VQ7C can understand, be respectively the proportional offset voltage of charge/discharge current I1 of the capacitor in VQ8C and VQ7C acquisition and the oscillating circuit therein in the scope that frequency of oscillation is low, thereby as shown in figure 10, when charge/discharge current I1 is constant, idle time is constant, and when charge/discharge current I1 more or less increased, also more or less increased idle time.

2) on the other hand, flow through therein in the scope of electric current I 3 (that is to say, therein in the scope that frequency of oscillation is high), idle time, DT was variable.Next its reason will be described.

In Fig. 9, in the scope that frequency of oscillation is low, electric current I 3 is zero, but in the scope that frequency of oscillation is high therein, electric current I 3 is flow through in the following manner therein.That is to say that when the emitter electromotive force of controlling the transistor Q02 of voltage as frequency of oscillation was lower than the electromotive force of contact DTADD, the transistor Q03 that is connected to terminal DTADD disconnected (therefore, not flowing through electric current I 3).Yet when the emitter electromotive force of controlling the transistor Q02 of voltage as frequency of oscillation was higher than the electromotive force of terminal DTADD, the transistor Q03 that is connected to terminal DTADD was switched on so that flow through electric current I 3.In Figure 10, in frequency of oscillation was lower than the scope of f1, electric current I 51 was fixed, and perhaps electric current I 52 more or less increases.Yet frequency of oscillation is higher than in the scope of f1 therein, has been that zero electric current I 3 beginnings are flow through suddenly till that time.Therefore, ammeter is shown I5=I1+I3.

Flow through therein in the scope of electric current I 3, electric current I 5 is expressed as:

I5＝I2+I4＝I1+I3

I5×R5＝I6×R6＝I7×R9＝(I1+I3)×R5

Therefore, the collector voltage of transistor Q8 and Q7 is expressed as expression formula (2) respectively:

VQ8C＝6V+VR8＝6V+(I1+I3)×R5×(R8/R6)

VQ7C＝6V-VR7＝6V-(I1+I3)×R5×(R7/R9)(2)

By the electric capacity of first capacitor 41 and second capacitor 42 is set, can in the circuit of (a), have omitted therein in the circuit of the 3rd capacitor 5 and obtain similar effects.

Above-mentioned expression formula (2) and Figure 10 according to VQ8C and VQ7C can understand, and the two obtains and electric current I 3 proportional offset voltages can be respectively VQ8C and VQ7C, so that electric current I 5 increases when electric current I 3 increases suddenly as shown in figure 10.(=I1+I3) function is represented, so the collector electrode electromotive force VQ8C of transistor Q8 and Q7 and VQ7C increase along with the increase of electric current I 5 because the collector electrode electromotive force VQ8C of transistor Q8 and Q7 and VQ7C are respectively by electric current I 5.Then, when collector electrode electromotive force VQ8C and VQ7C increased, collector electrode electromotive force VQ8C increased to and is higher than the position shown in Fig. 8, and collector electrode electromotive force VQ7C is reduced to and is lower than the position shown in Fig. 8.Therefore, the intersection point of VQ7C that DT begins to locate and triangular wave becomes more early in idle time, and idle time DT end VQ8C and the intersection point of triangular wave become more late.Therefore, idle time, DT increased to the width shown in being wider than.

Each example that Figure 11 shows above-mentioned (2) " when switching frequency surpassed preset frequency, idle time, DT increased continuously according to the increase of switching frequency ".Figure 12 shows above-mentioned (3) " when switching frequency surpasses preset frequency, idle time DT according to the increase of switching frequency and stepping increase " example.

In Figure 11 (a), when switching frequency was not higher than preset frequency f1, idle time, DT was (perhaps the increasing more or less) of fixing, and when switching frequency was not less than preset frequency f1, idle time, DT increased suddenly.

Figure 11 (b) shows the modified example of Figure 11 (a).

In Figure 11 (b) (one), make among Figure 11 (a) in the said fixing value of idle time at the switching frequency place that is not higher than preset frequency f1 or the value L1 that more or less increases and can be changed into L11, L12, L13, and make the idle time at the switching frequency place that is not less than preset frequency f1 DT the value L2 of unexpected increase can be changed into L21, L22, L23.

This can obtain by the ratio of 5 pairs of resistance R 6 of the change resistance R of the terminal DTMULTI place in Fig. 9.That is to say that according to relations I 5 * R5=I6 * R6, when R5 changed the ratio of R6, I5 had also changed the ratio of I6.Value I6 has defined value I7 and I8.Therefore, when I5 changed the ratio of I6, value I7 and I8 had also changed with respect to value I5, thereby have also changed with respect to the offset voltage of 6V.Therefore, idle time, DT also changed.In such a way, although for same frequency, idle time, DT still can change.

In Figure 11 (b) (two), make slope idle time of the predetermined switching frequency f1 among Figure 11 (a) can be changed into L24, L25, L26.

This slope depends on the combined electrical resistance at the R31 of resistance up and down and the R32 at contact DTADD place.When this combined electrical resistance was big, the electric current that flows out from Vcc did not flow in a large number.Therefore, this slope diminish (L26).On the contrary, when this combined electrical resistance hour, the electrorheological that flows out from Vcc is big.Therefore, this slope becomes big (L24).That is to say that when electric current I 3 flow through in a large number, electric current I 7 and I8 also increased widely.Therefore, the pressure drop of resistance R 7 and R8 change greatly consequently increases with respect to the offset voltage of 6V.Therefore, the collector voltage of transistor Q8 and Q7 increases according to above-mentioned expression formula (2).

Incidentally, when frequency of oscillation is high, there is the effect that idle time, DT narrowed down.Yet the increase of offset voltage is used for overcoming the effect of this frequency of oscillation and prolongs DT idle time.

In Figure 11 (b) (three), make the predetermined switching frequency f1 that in Figure 11 (a), plays the breakover point effect can be changed into f0, f2.

This breakover point can according in terminal DTADD up and down the resistance ratio of resistance R31 and R32 change.That is to say that this resistance ratio of resistance R 31 and R32 is corresponding to breakover point, this be because, the voltage that surpasses by this resistance ratio definition when the frequency of oscillation control voltage of the base stage that is applied to transistor q02 makes, electric current I 3 begins to flow through.When resistance R 31＞resistance R 32, the voltage of being determined by this resistance ratio is that so low consequently electric current I 3 begins to flow through more for a long time.When electric current I 3 flowed, electric current I 7 and I8 also flowed.Therefore, in resistance R 7 and R8, pressure drop occurs, so that increased with respect to the offset voltage of 6V.Therefore, the collector voltage of transistor Q8 and Q7 increases according to above-mentioned expression formula (2), so that idle time, DT just began to increase morning (f0).On the contrary, when resistance R 31＜resistance R 32, the voltage that is defined by this resistance ratio is so high, so that needs the longer time allow electric current I 3 begin to flow.Therefore, DT idle time later (f2) just begins to increase.

Figure 12 shows second embodiment of variable idle time of DT.

Figure 11 (a) shows such configuration, wherein idle time, DT had the border at the predetermined switching frequency f1 place of playing the breakover point effect, so that when switching frequency is not higher than f1, DT idle time fixing or more or less increase shown in L1, and when switching frequency was not less than f1, idle time, DT increased suddenly shown in L2.On the other hand, Figure 12 shows such configuration, and wherein DT was increased to f0, f1, f2 and f3 and increased to L3, L4, L5 and L6 respectively steppingly along with switching frequency idle time.

By using method, can easily obtain such stepping configuration as (one) among Figure 11 (b) described generation L11 idle time, L12 and L13.That is to say that resistance R 5 and resistance R 6 at the terminal DTMULTI place of Fig. 9 are formed by the variable resistor unit such as transistor etc., and the ratio between these variable resistor unit changes at the preset frequency place.Therefore, can obtain this stepping configuration.

Figure 13 shows the example of the oscillating circuit 23 among Fig. 5.

Oscillating circuit 23 has two comparators 231 and 232.The voltage V1 of divider resistance 235 is applied to the inverting input a (-) of comparator 231, and the voltage V2 of divider resistance 236 (supposition V1＞V2) is applied to the normal phase input end b (+) of comparator 232, and the voltage of capacitor 234 is applied to the sub-b of normal phase input end (+) of comparator 231 and the inverting input a (-) of comparator 232 simultaneously.

Output 0 when each comparator 231,232 is designed to electromotive force as its normal phase input end b (+) and is lower than the electromotive force of its inverting input a (-), output 1 when its electromotive force of normal phase input end b (+) is higher than the electromotive force of its inverting input a (-).

S end and R that

operational amplifier

231 and 232 output enter set-reset flip-floop 233 respectively hold.The charge/discharge circuit of capacitor 234 is formed by the output of the non-Q end of this set-reset flip-floop 233.

Therefore, when forming the charging circuit of capacitor 234 as shown in figure 13, the electromotive force of capacitor 234 increases now.Export the electromotive force of this capacitor 234.Utilize this, the electromotive force of the normal phase input end b (+) of comparator 231 increases.When the electromotive force of normal phase input end b (+) is higher than the electromotive force V1 of inverting input a (-), will exports 1 and be applied to the S end, and form the discharge circuit of capacitor 234 by the output of this non-Q end.After that, the electromotive force of capacitor 234 descends, and exports the electromotive force of this capacitor 234.Utilize this, the electromotive force of the normal phase input end b (+) of comparator 232 descends.When the electromotive force of normal phase input end b (+) is not higher than the electromotive force V2 of inverting input a (-), will exports 1 and be applied to the R end, and form the charging circuit of capacitor 234 by the output of this non-Q end.

In such a way, output is used for the charge/discharge electromotive force of capacitor 234, so that can obtain triangular wave oscillating circuit 23.In addition, the slope of this triangular wave is defined by the amplitude of charging current Ir.

Incidentally, the inverter circuit according to the high-frequency heating apparatus that is driven by two transistored bridges of the present invention is not limited to high-frequency heating apparatus shown in Figure 5.The present invention can be applicable to any inverter circuit, as long as this inverter circuit is to use the resonant circuit system that is formed the switching device of bridge arm by two transistors.

Figure 14 shows these inverter circuits of three types.

In Figure 14 (a), 1 pair of industrial power of DC power supply carries out full-wave rectification, so that direct voltage VDC is applied to the circuit that is connected in series of be connected in series circuit and first

semiconductor switching device

6 and 7 formation of second semiconductor switching device of

first capacitor

41 and 42 formation of second capacitor.The circuit that is connected in series that the elementary winding 3 of leakage transformer 2 and the 3rd capacitor 5 form is connected between the contact of the contact of first capacitor 41 and second capacitor 42 and first semiconductor switching device 6 and second semiconductor switching device 7.The control signal of self-driven part 8 offers the base stage of first semiconductor switching device 6 and second semiconductor switching device 7 respectively in the future.Idle time, generative circuit 24 was incorporated in the drive part 8.Incidentally, the primary side of not shown leakage transformer 2 and magnetron.

Then, also can realize smooth start and just be applied to this circuit in mode same as shown in Figure 5 so that obtain the low-limit frequency restricting circuits of the object of the invention with being used for.That is to say, in Fig. 5, if provide following circuit its will normally move, these circuit comprise: error signal generative circuit 21 is used to obtain at input current Iin with based on the difference between its reference current Ref; FM signal generative circuit 22 is used for generating FM signal according to this error signal generative circuit 21 and AC all-wave signal; Low-limit frequency restricting circuits 221 is used to realize smooth start so that obtain purpose of the present invention; Oscillating circuit 23 is used to generate triangular wave carrier; Idle time, generative circuit 24; Squaring circuit 25, be used for respectively according to the triangular wave output of oscillating circuit 23 and idle time generative circuit 24 output VQ7C and VQ8C form square wave; And switching device drive circuit 26, be used for generating the pulse that is used for this switching device of on/off according to the output of squaring circuit 25.

In such a way, might obtain such inverter circuit, wherein prevent the short circuit of power supply, thermal losses appears among the IGBT hardly, therefore do not have useless energy dissipation, and occur noise hardly, and wherein can realize smooth start by the ball bearing made using of adding the there to.

In Figure 14 (b), 1 pair of industrial power of DC power supply carries out full-wave rectification, so that direct voltage VDC is applied to the circuit that is connected in series that is connected in series circuit and is formed by first semiconductor switching device 6 and second semiconductor switching device 7 that elementary winding 3, first capacitor 5 and second capacitor 43 by leakage transformer 2 form.Between the contact of the contact of first capacitor 5 and second capacitor 43 and first semiconductor switching device 6 and second semiconductor switching device 7, form short circuit.The control signal of self-driven part 8 offers the base stage of first semiconductor switching device 6 and second semiconductor switching device 7 respectively in the future.Idle time, generative circuit 24 was incorporated in the drive part 8.Incidentally, the primary side of not shown leakage transformer 2 and magnetron.

Then, also can realize smooth start and just be applied to this circuit in mode same as shown in Figure 5 so that obtain the low-limit frequency restricting circuits of the object of the invention with being used for.That is to say, in Fig. 5, if provide following circuit its will normally move, these circuit comprise: error signal generative circuit 21 is used to obtain at input current Iin with based on the difference between its reference current Ref; FM signal generative circuit 22 is used for generating FM signal according to this error signal generative circuit 21 and AC all-wave signal; Low-limit frequency restricting circuits 221 is used to realize smooth start so that obtain purpose of the present invention; Oscillating circuit 23 is used to generate triangular wave carrier; Idle time, generative circuit 24; Squaring circuit 25, be used for respectively according to the triangular wave output of oscillating circuit 23 and idle time generative circuit 24 output VQ7C and VQ8C formation square wave; And switching device drive circuit 26, be used for generating the pulse that is used for the on/off switch device according to the output of squaring circuit 25.

Figure 14 (c) shows the circuit of indication full-bridge circuit.

In Figure 14 (c), 1 pair of industrial power of DC power supply carries out full-wave rectification, so that direct voltage VDC is applied to the circuit that is connected in series that is connected in series circuit and is formed by the 3rd semiconductor switching device 62 and the 4th semiconductor switching device 72 of first

semiconductor switching device

61 and 71 formation of second semiconductor switching device.The circuit that is connected in series that is formed by the elementary winding 3 and the 3rd capacitor 5 of leakage transformer 2 is connected between the contact of the contact of first semiconductor switching device 61 and second semiconductor switching device 71 and the 3rd semiconductor switching device 62 and the 4th semiconductor switching device 72.The 3rd capacitor 5 can omit.The control signal of self-driven part 8 offers the base stage of first semiconductor switching device 61, second semiconductor switching device 71, the 3rd semiconductor switching device 62 and the 4th semiconductor switching device 72 respectively in the future.Idle time, generative circuit 24 was incorporated in the drive part 8.Incidentally, the primary side of not shown leakage transformer 2 and magnetron.

Then, can also realize smooth start with being used for and just be applied to this circuit in mode same as shown in Figure 5 so that obtain the low-limit frequency restricting circuits of the object of the invention.That is to say, in Fig. 5, if provide following circuit its will normally move, these circuit comprise: error signal generative circuit 21 is used to obtain at input current Iin with based on the difference between its reference current Ref; FM signal generative circuit 22 is used for generating FM signal according to this error signal generative circuit 21 and AC all-wave signal; Low-limit frequency restricting circuits 221 is used to realize smooth start so that obtain purpose of the present invention; Oscillating circuit 23 is used to generate triangular wave carrier; Idle time, generative circuit 24; Squaring circuit 25, be used for respectively according to the triangular wave output of oscillating circuit 23 and idle time generative circuit 24 output VQ7C and VQ8C formation square wave; And switching device drive circuit 26, be used for generating the pulse that is used for the on/off switch device according to the output of squaring circuit 25.

Figure 15 illustrates according to the frequency of inverter circuit of the present invention diagram to phase characteristic.Among Figure 15, make the frequency 0 or 180 degree phase places that voltage is low therein neighbouring less, and bigger near 90 degree or 180 degree phase places.Therefore, near the 0 or 180 degree phase places that voltage is low, output current (voltage) increases the operating frequency characteristic according to the electric current among Fig. 1 therein, and this is low because of this frequency.On the contrary, near sufficiently high 90 degree of voltage or the 270 degree phase places, this frequency is maximized so that to the operating frequency characteristic output current (voltage) is narrowed down according to the electric current among Fig. 1 therein.Therefore, as shown in figure 16, spending on the phase range of 180 degree (spending to 360 degree from 180) from 0, output voltage becomes near a uniform voltage.

On the other hand, when the frequency shown in the dotted line F0 among Figure 15, among this figure does not change with respect to phase place to phase characteristic, even therein near the 0 or 180 degree phase places that voltage is low this frequency also be high.Therefore, to the operating frequency characteristic, output current (voltage) remains little according to the electric current among Fig. 1.Therefore, shown in the dotted line V1 among Figure 16, can not near 0 degree or 180 degree phase range, obtain enough voltage.

In addition, solid line F1 is the frequency-phase diagram under the error free situation, in this error free situation, is shifted so that the input current Ri (Fig. 5) of generation DC power supply equals reference current Ref from alternating current by CT.Solid line F2 is frequency-phase diagram in such cases, and wherein input current Ri is greater than reference current Ref, and increases so that reduce this electric current in the usable range of this frequency in Fig. 1.Solid line F3 is frequency-phase diagram in such cases, and wherein input current Ri is less than reference current Ref, and reduces so that increase this electric current in the usable range of this frequency in Fig. 1.

In Figure 16, the voltage waveform of solid line Vin indication industrial power.At the voltage waveform of the indication of the dotted line V1 on the Vin when carrying out switching with frequency all constant on all phase places.The voltage (secondary-side voltage of booster transformer) that solid line V0 indication obtains to this voltage V1 by the frequency modulation applications of inciting somebody to action as shown in figure 15.Account for voltage Vin, V1 and V0 on same figure are although so that there is big difference the ratio aspect between them, make them apparent.Dotted line V1 indication shown in the dotted line F0 among Figure 15, not have the secondary-side voltage constant frequency place, booster transformer of modulating.This waveform is not complementary with nonlinear magnetron load.On the other hand, when shown in the F1 among Figure 15, near this frequency 0 or 180 degree phase places that voltage is low therein, reducing and near 90 degree or 180 degree phase places, increasing, increase near output current (voltage) the 0 or 180 degree phase places that voltage is low therein, this output current (voltage) narrows down near 90 degree or 270 degree phase places simultaneously.Therefore, shown in the V0 among Figure 16,, generate constant voltage in the primary side of booster transformer from 0 any phase place of spending on the phase range of 180 degree (spending to 360 degree) from 180.This waveform and nonlinear magnetron load are complementary.

Incidentally, when switching device (IGBT) 6 and 7 is in load control following time, this, generative circuit also was effective aspect control idle time idle time.Control this idle time when central electrocardio presses 6V to change because collector voltage VQ7C and VQ8C can rise/descend interlocked with one anotherly, and can change (load control) on/off ratio between two transistor Q8 and Q7 by changing this 6V.That is to say that (each transistor is operated with 6V, and this is because of they power operations by 12V) exports the highest when the duty ratio between these two transistors is 50 pairs 50.When making this voltage be lower than 6V or being higher than 6V, these two transistorized collector voltage VQ7C and VQ8C can ground interlocked with one another rising/declines simultaneously, so that change the on/off ratio between these two transistors.Therefore, output has reduced.Yet even in this case, the offset voltage that generates in resistance R 8 and R7 does not change yet.Therefore, offset voltage remains unchanged.Therefore, should be appreciated that it is effective equally that this circuit changes idle time under the situation of load control.

As mentioned above, according to the present invention, be used for driving two semiconductor switching devices so that block direct current and have the function that restriction drives the low-limit frequency of the used frequency of these semiconductor switching devices with the driver element of output AC electric current thus.Above-mentioned low-limit frequency begins to locate to be set to height in the operation of high-frequency heating apparatus.After that, above-mentioned low-limit frequency is set to reduce gradually.Particularly, high-frequency heating apparatus comprises: the error signal generative circuit is used for basis at input current that exchanges industrial power and the difference generated error signal between the reference current; And the FM signal generative circuit, be used for proofreading and correct by above-mentioned AC power is carried out rectified voltage/redressed current that rectification obtains based on the output (error signal) of above-mentioned error signal generative circuit.The output of above-mentioned FM signal generative circuit is offered generative circuit idle time.Insert the low-limit frequency restricting circuits at above-mentioned FM signal generative circuit and above-mentioned idle time between the generative circuit.This low-limit frequency restricting circuits is based on the output signal of above-mentioned FM signal generative circuit, and limited frequency is offered above-mentioned idle time of generative circuit.Beginning the place in the operation of above-mentioned high-frequency heating apparatus, is the output that is higher than above-mentioned FM signal generative circuit with the frequency configuration that is provided with of low-limit frequency restricting circuits.According to beginning the over and done with time from operation, above-mentioned limited frequency reduces gradually.Along with the reduction of above-mentioned limited frequency,, and select higher signal in the output signal of the switching frequency of above-mentioned limited frequency and above-mentioned FM signal generative circuit as the signal that will offer above-mentioned idle time of generative circuit according to the over and done with time.Therefore, this selected signal is changed into the output signal of above-mentioned FM signal generative circuit gradually.In addition, above-mentioned low-limit frequency restricting circuits has capacitor.Above-mentioned capacitor charges during above-mentioned high-frequency heating apparatus pausing operation.In case above-mentioned high-frequency heating apparatus begins operation, just the voltage of this capacitor is offered above-mentioned idle time of generative circuit, and the electric charge that discharges and in this capacitor, accumulate.Therefore, might obtain such inverter circuit, wherein occur thermal losses among the IGBT hardly, therefore not have useless energy consumption, and occur noise hardly, and wherein can realize smooth start by simple circuit.

Though describe the present invention in detail with reference to specific embodiment, those skilled in the art can carry out various changes or modification, and not deviate from the spirit and scope of the present invention obviously as can be known in the present invention.

The Japanese patent application 2004-113272 that the application submitted to based on April 7th, 2004, the content of this Japanese patent application is incorporated at this by reference.

Industrial applicibility

According to high-frequency heating apparatus of the present invention, might obtain such inverter circuit, wherein prevent The short circuit of power supply occurs, occur hardly thermal losses among the IGBT, therefore do not have useless energy consumption, and And noise occurs hardly, and wherein can realize smooth start by the ball bearing made using of adding the there to.

Claims

1, a kind of high-frequency heating apparatus that is used to drive magnetron comprises:

DC power supply, it comprises AC power, is used for the voltage of this AC power is carried out the rectification circuit of rectification and is used for the smoothly smmothing capacitor of the output voltage of this rectification circuit;

Series circuit comprises two semiconductor switching devices, and described series circuit and described DC power supply are connected in parallel;

Resonant circuit is made of the elementary winding and the capacitor of leakage transformer, and an end of described resonant circuit is connected to the mid point of described series circuit, and the other end of described resonant circuit is connected to an end of described DC power supply;

Driver element is used for driving each of described semiconductor switching device;

Rectification unit is connected to the secondary winding of described leakage transformer;

Magnetron is connected to described rectification unit; And

Idle time, generative circuit was used for disconnecting simultaneously described semiconductor switching device,

Wherein said driver element has the function of the low-limit frequency of the frequency that restriction is used for driving described semiconductor switching device, so that described low-limit frequency is set to first frequency when the operation of this thermatron begins, and described low-limit frequency is set to the second frequency that after this progressively reduces with respect to this first frequency.

2, a kind of high-frequency heating apparatus that is used to drive magnetron comprises:

Two series circuits, each all comprises two semiconductor switching devices, and each in the described series circuit all is connected in parallel with described DC power supply;

Resonant circuit is made of the elementary winding and the capacitor of leakage transformer, and an end of described resonant circuit is connected to the mid point of one of described series circuit, and the other end of described resonant circuit is connected to the mid point of another series circuit;

Magnetron is connected to described rectification unit; And

Wherein said driver element has the function that restriction drives the low-limit frequency in the used frequency of described semiconductor switching device, so that described low-limit frequency is set to first frequency when the operation of this high-frequency heating apparatus begins, and described low-limit frequency is set to the second frequency that after this progressively reduces with respect to this first frequency.

3, a kind of high-frequency heating apparatus that is used to drive magnetron comprises:

Resonant circuit is made of the elementary winding and the capacitor of leakage transformer, and one of described resonant circuit and described semiconductor switching device are connected in parallel;

Magnetron is connected to described rectification unit; And

4, as any one the described high-frequency heating apparatus in the claim 1 to 3, also comprise:

The error signal generative circuit is used for basis at the input current of described AC power and the difference generated error signal between the reference current; And

The FM signal generative circuit, be used for based on error signal from described error signal generative circuit output, and proofread and correct rectified voltage or the redressed current that is obtained by the described AC power of rectification, wherein the output of described FM signal generative circuit is offered described idle time of generative circuit;

Wherein insert the low-limit frequency restricting circuits between the generative circuit at described FM signal generative circuit and described idle time, this low-limit frequency restricting circuits is based on the output signal of described FM signal generative circuit, and limited frequency is offered described idle time of generative circuit, so that the operation at above-mentioned high-frequency heating apparatus begins the place, with the frequency configuration that is provided with of low-limit frequency restricting circuits is the output that is higher than described FM signal generative circuit, and according to elapsed time after operation beginning, and progressively reduce described limited frequency, when reducing described limited frequency, according to elapsed time, higher signal between the switching frequency of the output signal of described FM signal generative circuit and described limited frequency is chosen as the signal that will offer described idle time of generative circuit, so that selected signal is changed into the output signal of described FM signal generative circuit gradually.

5, high-frequency heating apparatus as claimed in claim 4, wherein, described low-limit frequency restricting circuits has capacitor, described capacitor charges during the pausing operation of described high-frequency heating apparatus, and in case described high-frequency heating apparatus begins operation, just the voltage of this capacitor is offered described idle time of generative circuit, and the electric charge that in this capacitor, accumulates of discharge.

6, as any one the described high-frequency heating apparatus in the claim 1 to 3, wherein said idle time, generative circuit generated idle time fixing or that increase, and irrelevant with switching frequency.

7, as any one the described high-frequency heating apparatus in the claim 1 to 3, wherein, the described idle time that idle time, the generative circuit generation increased along with the increase of switching frequency.

8, high-frequency heating apparatus as claimed in claim 7, generative circuit was fixed at the predetermined switching frequency place that is not higher than preset frequency or was increased described idle time wherein said idle time.

9, high-frequency heating apparatus as claimed in claim 7, wherein, described idle time, generative circuit increased described idle time suddenly at the predetermined switching frequency place that is not less than preset frequency.

10, high-frequency heating apparatus as claimed in claim 8, wherein, the value fixing or that increase in described idle time at the predetermined switching frequency place that is not higher than preset frequency is variable.

11, high-frequency heating apparatus as claimed in claim 9 wherein, is variable in the value of the unexpected increase of described idle time at the predetermined switching frequency place that is not less than preset frequency.

12, high-frequency heating apparatus as claimed in claim 8, the value of wherein said predetermined switching frequency is variable.

13, as any one the described high-frequency heating apparatus in the claim 1 to 3, wherein said idle time, generative circuit increased idle time steppingly along with the increase of switching frequency.

14, as any one the described high-frequency heating apparatus in the claim 1 to 3, wherein said idle time, generative circuit generated idle time based on the positive and negative offset voltage, in the described positive and negative offset voltage each is to change with proportional first gradient of the increase of switching frequency, and when this switching frequency reaches preset frequency or when higher, changes with second gradient.

15, as any one the described high-frequency heating apparatus in the claim 1 to 3, wherein said idle time, generative circuit comprised: the VCC power supply; Load control power supply; First electric current changes pro rata with switching frequency; Second electric current, beginning is flowed at the preset frequency place and is changed pro rata with this switching frequency; The 3rd electric current, by with described first electric current and second electric current and multiply each other with pre-determined factor and to obtain; And high and low potential generation unit, be used for generating one group of height and low potential by adding respectively that described load control power supply obtains to the proportional positive and negative offset voltage of described the 3rd electric current, and based on described one group high and low potential generation idle time.

16, high-frequency heating apparatus as claimed in claim 15 wherein by changing at least one in described load control power source voltage and the described switching frequency, is carried out the control of input power or input current.